This invention relates to photographic equipment and more particularly, it concerns an improved system for processing and ejecting photographic film units of a type in which a film unit carried supply of processing fluid is spread over an area of exposed photosensitive materials as the unit is passed from the interior of a camera designed to handle such units.
Camera systems in which film units may be exposed and processed instantly on withdrawal or ejection of the exposed unit from a camera are now well known in the art. In general, such systems include a pair of spread rollers or equivalent means to establish a pressure nip through which each film unit is passed after exposure in order to rupture a unit carried pod of processing fluid and spread the fluid uniformly over the exposed photographic materials, usually lying at the interface of a pair of sheets in the unit, so that the latent image formed by exposure of such materials will be developed into a real or visual photographic image. In early systems, each film unit was provided or associated with some form of pull tab accessible at the camera exterior and which, when pulled manually, effected a withdrawal of the associated film unit through the aforementioned pressure nip. More recently, instant camera systems have become available in which improved film units are ejected from the camera, again through a processing fluid spreading pressure nip, by a motor-driven system. A principal advantage of the more recent of these systems is that they are "trash free"; that is, only the film unit is discharged from the camera with no pull tab or other discardable material accompanying the unit structure providing the final photograph.
Motor-driven processing fluid spreader systems for instant cameras possess several additional advantages which are important to film unit processing. For example, the speed at which the film unit is passed through the pressure nip can be controlled very accurately. This is important not only from the standpoint of assuring the uniform spread of processing fluid over the area of the exposed photographic materials contained in the unit, but also from the standpoint of controlling the length of time that infinitely successive increments of the film unit remain protected from light within the camera structure after processing fluid has been spread over such increments. In other words, the short duration of time between contact by the processing fluid and exit from the camera into ambient light permits the film to become insensitive to light before exiting from the camera. Equally as important as control over the rate of film unit feed through the pressure nip is that the driving force for feeding the unit is applied directly at the pressure nip by the rotatably driven rollers in a manner to avoid any film unit stresses which would interfere with uniform spreading of the processing fluid.
On the other hand, motor-driven processing fluid spreading systems for instant cameras suffer from such disadvantages as manufacturing costs, complexity of component packaging within the camera and need for a source of electrical energy of sufficient capacity to meet the power requirements of the motor drive. Additionally, it is necessary for at least one of the pressure nip defining rollers to be finished with a traction or friction surface so that rotation of the roller will be translated into linear movement of the film unit. Although all of these disadvantages have been overcome as is evidenced by instant camera systems available commercially at the present time, the success of the presently available systems has involved a measure of compromise in system costs. There is a need, therefore, for a manually actuated processing fluid spreader system for instant cameras by which costs incident to electric motor drives can be avoided but without compromise in the overall effectiveness of system operation.